Is there a way to display a pop-up message box in PowerShell that is compatible with both Windows systems and MacOS?

The Show-MessageBox function defined below offers message-box functionality on both Windows and macOS, modeled on the WinForms MessageBox class.

Examples:

# Message box with custom message, OK button only, and default title and icon$null = Show-MessageBox 'some message'# Message box with custom message and title, buttons OK and cancel, and # the Stop icon (critical error)# Return value is the name of the button chosen.$buttonChosen = Show-MessageBox 'some message' 'a title' -Buttons OKCancel -Icon Stop

The syntax (spread across multiple lines for readability):

Show-MessageBox [-Message] <string> [[-Title] <string>]                 [[-Buttons] {OK | OKCancel | AbortRetryIgnore | YesNoCancel | YesNo | RetryCancel}]                 [-Icon {Information | Warning | Stop}]                 [-DefaultButtonIndex {0 | 1 | 2}]

Note:

• On macOS, AppleScript's display alert command is used to create the message box.

  • While this command nominally distinguishes between severities informational, warning, and critical, the former two show the same icon - a folder - and the latter overlays the folder icon only with an exclamation mark.

• For cross-platform consistency the output value is a string, namely the name of the button pressed by the user.

• -DefaultButtonIndex is the 0-based index of the button that will be pressed when the user just presses Enter.

  • Windows: If a Cancel button is present, Esc presses it.
  • macOs: If a No, Abort or Cancel button is present and it isn't the default button, Esc presses it.

Show-MessageBox source code:

function Show-MessageBox {  [CmdletBinding(PositionalBinding=$false)]  param(    [Parameter(Mandatory, Position=0)]    [string] $Message,    [Parameter(Position=1)]    [string] $Title,    [Parameter(Position=2)]    [ValidateSet('OK', 'OKCancel', 'AbortRetryIgnore', 'YesNoCancel', 'YesNo', 'RetryCancel')]    [string] $Buttons = 'OK',    [ValidateSet('Information', 'Warning', 'Stop')]    [string] $Icon = 'Information',    [ValidateSet(0, 1, 2)]    [int] $DefaultButtonIndex  )  # So that the $IsLinux and $IsMacOS PS Core-only  # variables can safely be accessed in WinPS.  Set-StrictMode -Off  $buttonMap = @{     'OK'               = @{ buttonList = 'OK'; defaultButtonIndex = 0 }    'OKCancel'         = @{ buttonList = 'OK', 'Cancel'; defaultButtonIndex = 0; cancelButtonIndex = 1 }    'AbortRetryIgnore' = @{ buttonList = 'Abort', 'Retry', 'Ignore'; defaultButtonIndex = 2; ; cancelButtonIndex = 0 };     'YesNoCancel'      = @{ buttonList = 'Yes', 'No', 'Cancel'; defaultButtonIndex = 2; cancelButtonIndex = 2 };    'YesNo'            = @{ buttonList = 'Yes', 'No'; defaultButtonIndex = 0; cancelButtonIndex = 1 }    'RetryCancel'      = @{ buttonList = 'Retry', 'Cancel'; defaultButtonIndex = 0; cancelButtonIndex = 1 }  }  $numButtons = $buttonMap[$Buttons].buttonList.Count  $defaultIndex = [math]::Min($numButtons - 1, ($buttonMap[$Buttons].defaultButtonIndex, $DefaultButtonIndex)[$PSBoundParameters.ContainsKey('DefaultButtonIndex')])  $cancelIndex = $buttonMap[$Buttons].cancelButtonIndex  if ($IsLinux) {     Throw "Not supported on Linux."   }  elseif ($IsMacOS) {    $iconClause = if ($Icon -ne 'Information') { 'as ' + $Icon -replace 'Stop', 'critical' }    $buttonClause = "buttons { $($buttonMap[$Buttons].buttonList -replace '^', '"' -replace '$', '"' -join ',') }"    $defaultButtonClause = 'default button ' + (1 + $defaultIndex)    if ($null -ne $cancelIndex -and $cancelIndex -ne $defaultIndex) {      $cancelButtonClause = 'cancel button ' + (1 + $cancelIndex)    }    $appleScript = "display alert `"$Title`" message `"$Message`" $iconClause $buttonClause $defaultButtonClause $cancelButtonClause"            #"    Write-Verbose "AppleScript command: $appleScript"    # Show the dialog.    # Note that if a cancel button is assigned, pressing Esc results in an    # error message indicating that the user canceled.    $result = $appleScript | osascript 2>$null    # Output the name of the button chosen (string):    # The name of the cancel button, if the dialog was canceled with ESC, or the    # name of the clicked button, which is reported as "button:<name>"    if (-not $result) { $buttonMap[$Buttons].buttonList[$buttonMap[$Buttons].cancelButtonIndex] } else { $result -replace '.+:' }  }  else { # Windows    Add-Type -Assembly System.Windows.Forms            # Show the dialog.    # Output the chosen button as a stringified [System.Windows.Forms.DialogResult] enum value,    # for consistency with the macOS behavior.    [System.Windows.Forms.MessageBox]::Show($Message, $Title, $Buttons, $Icon, $defaultIndex * 256).ToString()  }}